US3084543A - Pitot tube - Google Patents

Description

A ril 9, 1963 c. w. FINKL ETA]. 3,084,543

PITOT TUBE Filed June 1, 1959 IN V EN TORS Uni atent 3,084,543 PITOT TUBE Charles W. Finkl and Arthur Carlson, Chicago, lib, as-

signors, by mesne assignments, to Attwood Corporation, a corporation of Michigan Filed June 1, 1959, Ser. No. 817,342 11 Claims. (Cl. 73-182) Our invention relates generally to water speed measuring devices and particularly to a new and improved Pitot tube for water speed indicators.

Pitot tubes for pleasure boat Water speed indicators are generally mounted on the boat near the bottom of the transom. A water passage extends through the tube and has an admission port opening in the direction of boat travel at the lower end. The upper end opens into a conduit leading to a pressure gauge. As the boat moves forward, water flows up the passage and through the conduit to the pressure gauge which is calibrated in water speed units.

Pitot tubes are generally one of the lowest hanging projections from the boat. They should be able to kick upwardly upon contact with floating driftwood, dead heads or other underwater objects and then swing back down into a centered or equilibrium condition to provide a continuously accurate reading. In efiect, the tube must automatically reset itself after the disrupting object has passed. The tube must also be capable of being mounted on transoms of varying angles, must maintain perfectly horizontal alignment even when the boat porpoises or changes its planing angle, and must be ble to shed weeds easily.

Most present Pitot tubes generally utilize a spring arrangement for resetting the tube after a foreign object passes. These tubes are subject to failure due to repeated flexure from impact with underwater objects and the action of the water on the tube. After a time the spring constant decreases to a point where it may not be able to hold the tube perfectly horizontal and false readings result.

Accordingly, a primary object of this invention is to provide a Pitot tube which utilizes water forces acting on the tube to maintain it properly positioned at all speeds.

Another object is to provide a light, compact Pitot tube which swings up on impact with a foreign object in the water and automatically resets itself as the object passes by without the use of springs.

Another object is to provide a Pitot tube which may be mounted on a transom of any angle.

Yet another object is to provide a Pitot tube which stays in perfect alignment even though the boat porpoises or changes its planing angle.

Yet a further object is to provide a Pitot tube which may be fabricated from inexpensive plastic material.

Another object is to provide a combination hydraulicpneumatic Pitot tube assembly having a pressure stabilizer which instantly and accurately reflects changes in speed.

Other objects and advantages of our invention will become apparent from the following description taken in connection with the accompanying drawings wherein by way of illustration and example certain embodiments of the invention are set forth.

Our invention is illustrated more or less diagrammatically in the accompanying drawings wherein:

FIGURE 1 is a side view of our Pitot tube mounted on the lower portion of a transom;

FIGURE 2 is a rear view of the Pitot tube of FIG- URE 1;

FIGURE 3 is a bottom view of the Pitot tube of FIG- URE 1;

' the bottom as illustrated in FIGURE 1.

FIGURE 4 is a side view of another embodiment of our Pitot tube illustrating a pressure stabilizing tank; and

FIGURE 5 is a bottom view of the Pitot tube of FIG- URE 4.

Like reference numerals will be used to indicate like parts throughout the specification and drawings.

In FIGURE 1, our Pitot tube is indicated generally at 10. It includes a body or shank portion :11, a mounting ear 12 at the upper inner edge of the shank portion, and a foot or paravane 13 at the bottom. The shank portion 11 has knife edges 14 and 15 on the leading and trailing edges respectively to present minimum water resistance. Trailing edge 15 is contoured into the paravane to provide non-turbulent water flow. A splash plate 16 deflects the water downwardly as the tube moves through the water.

Paravane 13 in this instance is roughly in the form of an isosceles triangle with the apex of the equal sides terminating near the bottom of leading edge 14. Top surface 17 is slightly inclined from the horizontal to form a sharp edge with bottom surface 18 as at 19.

Water passage or aperture 29 extends through the body. Admission port 21 opens into the blunt end of thickened portion 22 of the vane. Outlet 23 at the top of the body is adapted for connection to a water speed indicator. The sharp edge 19 extends horizontally outwardly on each side of the blunt end of thickened portion 22 so the paravane will more readily dig into the water after having been kicked upwardly.

The Pitot tube is secured to transom 24 by an automatic reset clip indicated generally at .25. The clip includes a roughly oval shaped back plate 26 and a pair of parallel ears 27 and 28. The ears form a slot 29 slightly larger than the width of mounting ear 12. Each clip ear has an inwardly and downwardly tapered recess 30, 31 opening into circular recesses 32, 33. The bottom width of the tapered recesses may be slightly smaller than the diameter of the circular recess. Pivot pin 34 which may be fixed or rotatable in mounting ear 12 slips into the circular recesses 32, 33 to permit swinging movement of the tube. Screws 37 fasten the bracket to the transom.

A variation of our invention is illustrated in FIGURES 4 and 5. Circular platform 40 rests on splash plate 16 and a fluid tight pressure stabilizing or static tank 41 is secured thereto. Hose 42 connects the tank to any suitable water speed indicator 43-.

The water aperture 44 in this instance slants upwardly from the inlet port '45 through the circular platform 40 and opens into the tank. This eliminates the elbow at The leading edge of paravane 50, which is considerably larger than paravane 13, is streamlined as at 51 to reduce water resistance. The trailing edge is extended as at 52 for a purpose which will appear hereafter.

The use and operation of the invention is as follows:

Pitot tubes determine the speed of a boat relative to the water by measuring the impact or force of the water on the tube. The magnitude of the force varies roughly proportionally to the square of the relative boat-water speed as expressed by the formula V= /2-gh where V is feet/ second, g is gravity, and h is head of water in feet. The force is then transmitted to a pressure gauge calibrated to read directly in water speed units.

In FIGURE 1, water enters the tube through inlet port 21, passes upwardly through passage 20 and enters a hose connected to outlet port 23 leading to a pressure gauge (not shown). No matter what speed the boat is moving through the water, the tube will maintain the position of FIGURE 1 and 2 for the following reason.

Force vector R represents the reaction of the center of pressure of the water on the vane 13. This value be mathematically determined from the dimensions and angle of incidence of the vane. X represents the distance from the pivot point P to the point at which R acts on vane 13. Force vector Cl? represents the force acting against that portion of the Pitot tube against whicl the water impinges. For convenience of illustration, all the force is illustrated as acting through the center of pressure which can be mathematically determined once the dimensions of the Pitot tube are known. Y repre sents the perpendicular distance between the pivot point P and the center of pressure.

counterclockwise moment RX must equal clockwise moment (CP) Y for the Pitot tube to remain in the position of FIGURE 1. This condition of equilibrium will always be attained because as the tube swings either rearwardly or forwardly, the moments become unbalanced with the larger moment always acting in an equilibrium restoring direction.

If an unbalanced condition occurs whereby the Pitot tube moves rearwardly, the tube swings clockwise about pin 34. Force R will increase since the angle of incidence of vane 13 increases. Distance X also increases. At the same time force (CP) decreases since the effective area of the body portion decreases as it swings upwardly from its FIGURE 2 position. Distance Y also decreases. The larger counterclockwise moment XR then swings the tube back to the FIGURE 1 position.

Similarly, should the tube swing forward for any reason as for example when the mounting bracket is secured to an upwardly and rearwardly inclined transom, X decreases, force R acts in a reverse direction and both Y and (CP) increase, thus setting up unbalanced clockwise moments. These unbalanced moments quickly reposition the tube.

A pneumatic-hydraulic pressure stabilized tube assembly is illustrated in the embodiment of FIGURES 4 and 5. When water alone is utilized the water speed indicator tends to read slow because the pressure gauge 43 is not instantly responsive to changes in water pressure resulting from changes in boat speed. This is because the static head of water must rise from the level of the tube to the pressure gauge before the needle is actuated. Static tank 41 converts the static head to a more sensitive combined hydraulic-pneumatic head. As the water level in tank 41 rises, which will occur substantially instantaneously with changes in boat speed because of the relatively short passage 44, the air in the space above water W will be simultaneously compressed. The change in air pressure is then instantly read on air pressure responsive gauge 43.

Extended portion 52 of paravane 50 increases the downwardly acting force R to more quickly reposition the tube. Additional vanes may be added if needed.

Since the Pitot tube assembly automatically resets itself solely in response to water forces acting on it, no springs are needed to return it to normal operating position. Consequently mounting bracket 25 may be made of inexpensive plastic materials which do not induce electrolytic deterioration of the hull. The tube itself may be molded from plastic since no inherent spring action is required.

The downwardly and rearwardly tapered leading edge sheds weeds and presents a sliding edge to driftwood, dead heads and other underwater objects whereby the tube may be kicked up without any possibility of binding or catching upon the object.

As will be readily apparent to one skilled in the art, the Pitot tube should be located in a position in which it is exposed only to undisturbed water flow. It is well known, for example, that the area of turbulence formed behind a propeller is cone shaped, and hence it is desirable to position the Pitot tube out of this turbulent cone shaped area for most accurate readings. Similarly, the tube should not be positioned in the turbulent area directly behind any downwardly hanging obstruction.

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Other variations will be apparent to those slc lled in the art. For example, any suitable structure may be utilized to permit free swinging movement of the assembly about the pivot point P. We have formed spherical segments I on either side of the mounting ear 1?. in place of Pivot pin 34 for example.

The foregoing description is illustrative only and not definitive. Accordingly, our invention should not be limited except by the scope of the following appended claims.

We claim:

1. An automatically self stabilizing Pitot tube which utilizes water forces to maintain it properly positioned at *all speeds and planing angles of the boat to which it is attached, said Pitot tube including a body member adapted to be pivotally mounted to a boat whereby a portion of the member is submerged, said member having a passage extending therethrough, said passage having a water admission port in the submerged portion opening substantially in the direction of travel of the boat and an outlet adapted to be connected to a suitable gauge, and a generally horizontally oriented paravane on the submerged portion of the body, said paravane being so positioned that the moment tending to swing the tube about the pivot in one direction due to the downwardly acting force on the paravane balances the moment tending to swing the tube about the pivot in the opposite direction due to the rearwardly acting force of the water when the boat moves relative to the water.

2. The Pitot tube of claim 1 further including a mounting member adapted to be secured to a boat, the Pitot tube being pivotally mounted in the mounting member.

3. The Pitot tube of claim 1 in which the water admission port is in the leading edge of the paravane.

4. The Pitot tube of claim 3 in which the paravane diverges outwardly rearwardly, the leading edge having a thickened center portion in which the water admission port is formed flanked by knife edges to facilitate reentry of the paravane into the water after being kicked upwardly.

5. The automatically self-stabilizing Pitot tube of claim 1 further characterized in that the paravane is formed with a rearwardly, upwardly inclined top surface.

6. The Pitot tube assembly of claim 1 further characterized in that the passage has a substantially straight run from the water admission port to the outlet.

7. A Pitot tube assembly for use with a water speed indicator, said assembly including, in combination, a body member adapted to be pivotally mounted on a boat whereby a portion of the body member is submerged, said member having a passage extending therethrough, said passage having its inlet in the submerged portion opening substantially in the direction of travel of the boat and its outlet opening into a pressure stabilizing tank communicating with the outlet, said tank having an air outlet adapted for connection to an air pressure responsive water speed indicator, and a vane on the submerged portion of the body member, said vane being so positioned that the moment tending to swing the assembly about the pivot in one direction due to the downwardly acting force on the vane balances the moment tending to swing the assembly about the pivot in the opposite direction due to the rearwardly acting force of the water when the boat moves relative to the Water.

8. The Pitot tube assembly of claim 7 further characterized in that the passage has a substantially straight run from its inlet to the outlet communicating with the tank.

9. The Pitot tube assembly of claim 7 further characterized in that the inlet is in the leading edge of the vane, and further including a splash plate near the upper edge of the submerged portion of the body member.

10. An automatically self stabilizing Pitot tube which utilizes water created pressure forces to maintain it properly positioned at all speeds and planing angles of a boat to which it is attached and which automatically re- 5 r sets itself after encountering an obstruction, said Pito tube including, in combination,

a body member having a passage therein, said passage having a water admission port opening in the direction of boat travel and an outlet adapted for connection to a pressure responsive speed indicating device,

pivot means for mounting the body member to the boat, said pivot means being arranged to enable the body member to swing freely in response to impact with objects in its path of movement and to changes in position and planing angle of the boat, at least that portion of the body member having the water admission port therein being constructed and arranged to be submerged at all times during normal, unimpeded operation,

a generally horizontally oriented paravane near the bottom of the submerged portion,

said paravane being effective, due to water forces acting thereagainst, to induce a moment tending to swing the Pitot tube about the pivot means in opposition to a moment tending to swing the Pitot tube in the opposite direction due to water forces acting against the submerged portion of the Pitot tube.

11. The automatically self stabilizing Pitot tube of claim 10 further characterized in that the water admission port opens into the leading edge of the paravane, said leading edge having a thickened center portion in which the water admission port is formed flanked by sharp edges which facilitate re-entry of the paravane into the water after having been kicked upwardly.

References Cited in the file of this patent UNITED STATES PATENTS 382,362 Hogg May S, 1888 672,123 Delanoy Apr. 16, 1901 1,099,206 Sanborn June 9, 1914 1,955,502 Kenyon Apr. 17, 1934 2,617,297 Moore Nov. 11, 1952

Claims (1)

10. AN AUTOMATICALLY SELF STABILIZING PITOT TUBE WHICH UTILIZES WATER CREATED PRESSURE FORCES TO MAINTAIN IT PROPERLY POSITIONED AT ALL SPEEDS AND PLANING ANGLES OF A BOAT TO WHICH IT IS ATTACHED AND WHICH AUTOMATICALLY RESETS ITSELF AFTER ENCOUNTERING AN OBSTRUCTION, SAID PITOT TUBE INCLUDING, IN COMBINATION, A BODY MEMBER HAVING A PASSAGE THEREIN, SAID PASSAGE HAVING A WATER ADMISSION PORT OPENING IN THE DIRECTION OF BOAT TRAVEL AND AN OUTLET ADAPTED FOR CONNECTION TO A PRESSURE RESPONSIVE SPEED INDICATING DEVICE, PIVOT MEANS FOR MOUNTING THE BODY MEMBER TO THE BOAT, SAID PIVOT MEANS BEING ARRANGED TO ENABLE THE BODY MEMBER TO SWING FREELY IN RESPONSE TO IMPACT WITH OBJECTS IN ITS PATH OF MOVEMENT AND TO CHANGES IN POSITION AND PLANING ANGLE OF THE BOAT, AT LEAST THAT PORTION OF THE BODY MEMBER HAVING THE WATER ADMISSION PORT THEREIN BEING CONSTRUCTED AND ARRANGED TO BE SUBMERGED AT ALL TIMES DURING NORMAL, UNIMPEDED OPERATION, A GENERALLY HORIZONTALLY ORIENTED PARAVANE NEAR THE BOTTOM OF THE SUBMERGED PORTION, SAID PARAVANE BEING EFFECTIVE, DUE TO WATER FORCES ACTING THEREAGAINST, TO INDUCE A MOMENT TENDING TO SWING THE PITOT TUBE ABOUT THE PIVOT MEANS IN OPPOSITION TO A MOMENT TENDING TO SWING THE PITOT TUBE IN THE OPPOSITE DIRECTION DUE TO WATER FORCES ACTING AGAINST THE SUBMERGED PORTION OF THE PITOT TUBE.

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